In uplink of W-CDMA, signals from user equipments (UE) in the same cell are multiplied by scramble codes specific to users and signals received in base station is non-orthogonal. Therefore fast transmission power control (TPC) is essential to reduce the multi-user interference (i.e. the near-far problem).
Meanwhile, in the LTE (Long Term Evolution) system defined by 3 GPP Release 8 (hereinafter, referred to as “Rel-8 LTE”), in uplink is adopted SC-FDMA (Single-Carrier Frequency Division Multiple Access) radio access that actualizes low Peak-to Average Power Ratio (PAPR) and that is effective at increasing coverage. Accordingly, by scheduling in the base station, basically, since radio resources of frequency and time domains are assigned to a single UE, orthogonality in the frequency and time domains is achieved among users in the same cell. Therefore, from the viewpoint of suppressing multi-user interference in the same cell, fast TPC is not always essential. However, in Rel-8 LTE, since one-cell reuse is basically adopted, interference from adjacent cells is significant, and particularly, the interference level from the UE existing at the cell edge is high. Therefore, it is necessary to apply TPC also in LTE to compensate for such adjacent-cell interference and to obtain the required reception quality.
In uplink based on Rel-8 LTE are defined 1) Physical Random Access Channel (PRACH), 2) Physical Uplink Shared Channel (PUSCH), and 3) Physical Uplink Control Channel (PUCCH). Particularly, the PUSCH is, a physical channel to transmit user data, applied frequency domain scheduling for assigning frequency blocks with high received signal levels to each user optimally based on adaptive modulation and channel coding (AMC) corresponding to the received channel state. To respond to the instantaneous fading variation, fast frequency domain scheduling and fast AMC is executed for each TTI (Transmission Time Interval) with a length of 1 msec. In this case, it is possible to respond to the instantaneous fading variation by adaptive rate control using AMC, and slow TPC is used to respond to propagation loss from the base station and variations in adjacent-cell interference. The transmission power control of the PUSCH in uplink is controlled by a combination of open-loop TPC based on parameters (Po, α, etc.) notified from the base station at relatively long intervals and a propagation loss value measured by the mobile station, and closed-loop TPC based on intermediate variations of the received signal level due to shadowing and TPC command notified at relatively short intervals to compensate for a setting error in transmission power in the UE (3GPP, TS36. 213). In closed-loop TPC between the base station and mobile station, for example, the base station calculates a difference value between the reception SINR (Signal to Interference plus Noise Ratio) averaged by a time period t and target SINR, notifies the difference value as a TPC command to the mobile station, and thus controls the transmission power in the mobile station.
Citation List
Non-Patent Literature
    Non-patent Literature 1    3GPP, TS 36.213, V8.2.0, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures”